What medications are known to cause hair loss?

Drug-induced hair loss represents a significant side effect that can impact quality of life and the ability to continue treatment. In this article, we will examine medications associated with hair loss, their mechanisms of action, and the various drug classes implicated in this adverse effect. While most medication-induced hair loss (alopecia) is reversible upon discontinuation of the causative agent, understanding which drugs pose this risk is essential for both healthcare providers and patients.

Why Do Some Medications Cause Hair Loss?

Medications can trigger hair loss through two primary mechanisms: telogen effluvium and anagen effluvium. Each affects the hair growth cycle differently. Other causes include changes in the immune system and inflammation.

Telogen Effluvium

Telogen effluvium represents the most common type of drug-induced hair loss. This condition typically appears within 2 to 4 months after starting the medication and causes hair follicles to prematurely enter their resting (telogen) phase and fall out too soon. In normal hair growth, only about 10% of follicles are in the telogen phase, but medications can disrupt this balance, leading to excessive shedding. People experiencing telogen effluvium may shed between 30% to 70% more than the normal 50-100 hairs per day. The delayed onset between medication initiation and noticeable hair loss often makes it challenging to identify the causative agent, as patients may not connect their hair loss to a medication started months earlier.

Anagen Effluvium

Anagen effluvium occurs during the active growth phase of hair and typically develops much more rapidly-within days to weeks after medication exposure. This type of hair loss prevents matrix cells from dividing normally, thereby inhibiting new hair production. Chemotherapy drugs commonly cause anagen effluvium, which can be severe, resulting in loss of most or all scalp hair, eyebrows, eyelashes, and other body hair. The severity and rapidity of onset make anagen effluvium particularly distressing for patients, though it often resolves after completing treatment.

Alopecia areata

Rarely, some medications such as monoclonal antibodies that target cytokines (e.g., TNF-alpha and interleukin-4 antagonists) can cause a condition called alopecia areata (AA). It isn’t fully clear how these medications sometimes cause AA, but it might have to do with changes in the hair follicle cells.

Scarring alopecia

Another rare form of hair loss from certain medications is scarring alopecia. This condition is thought to be caused by inflammatory chemicals triggered by some medications.

Common Medication Categories Associated with Hair Loss

1. Chemotherapy and Cancer Treatments

Chemotherapy agents are well-established causes of hair loss, primarily through anagen effluvium. Several medications have strong evidence supporting their association with alopecia.

• Docetaxel, capecitabine, erlotinib, imatinib, and bortezomib have all been identified in studies with strong levels of evidence linking them to hair loss.
• These medications target rapidly dividing cells, including hair follicle cells, explaining their profound effect on hair growth.
• The hair loss typically begins within days to weeks after treatment initiation and can affect the entire body.

While distressing, patients can often be reassured that hair regrowth typically occurs after completing treatment, though texture and color may initially differ.

2. Antibiotics and Antimicrobials

• Some antibiotics, such as rifampicin and isoniazid, have been reported to cause hair loss in case reports.
• Antifungal medications, such as anidulafungin and itraconazole, have also been implicated in medication-induced telogen effluvium.
• Certain antiviral medications, such as tenofovir alafenamide and ribavirin, have been reported to cause hair loss in case reports.

3. Psychiatric and Neurological Medications

Several psychotropic medications have been associated with hair loss, with valproate derivatives being particularly well-documented culprits. Valproate is notorious for medication-induced hair loss, with alopecia listed among its most common adverse reactions (occurring in >5% of patients). A systematic review and meta-analysis estimated the overall incidence of valproate-related alopecia to be approximately 11%.

The proposed mechanism for valproate-induced hair loss includes chelation of zinc and selenium, as well as reduced serum biotinidase activity, which decreases the availability of essential micronutrients required for hair growth. Valproate-related hair loss typically presents as diffuse and nonscarring, often appearing 3 to 6 months following medication initiation.

Lamotrigine, used to treat epilepsy and bipolar disorder, has also shown evidence of association with alopecia. Certain antidepressants, such as bupropion and imipramine, have also been linked to hair loss. Additionally, patients taking some antipsychotics (e.g., haloperidol) have reported hair loss as a side effect.

4. Cardiovascular Medications

Anticoagulants

Both traditional anticoagulants and newer direct oral anticoagulants (DOACs) have been implicated in hair loss. Sometimes called blood thinners, these medications help prevent and treat blood clots.

Heparin and warfarin are known to cause alopecia, likely through a telogen effluvium mechanism. The observation that both medication classes cause similar patterns of hair loss suggests a shared mechanism related to their anticoagulant activity.
Emerging evidence indicates that DOACs, including rivaroxaban, dabigatran, and apixaban, may also cause hair loss.

The World Health Organization's pharmacovigilance database (VigiBase) has received 405 reports of DOAC-associated alopecia: 143 for rivaroxaban, 215 for dabigatran, 47 for apixaban. A prospective study following 37 patients prescribed rivaroxaban or dabigatran found that one patient discontinued rivaroxaban after two weeks due to tiredness and hair loss.

Beta Blockers

Beta blockers can cause telogen effluvium, though this side effect does not happen often. Medications in this class associated with hair loss include propranolol (Inderal), atenolol (Tenormin), and metoprolol. The mechanism may be related to reduced blood flow to hair follicles or disruption of normal hair cycle signaling.

Angiotensin‐converting enzyme (ACE) inhibitors

All ACE inhibitors have also been connected to hair loss as a potential side effect. More research is needed to understand if some tend to cause hair loss more than others.

5. Immunomodulators and Biologics

Several immunomodulating agents have strong evidence linking them to hair loss. Adalimumab and infliximab, both TNF-alpha inhibitors used to treat autoimmune conditions, have been associated with alopecia in studies with strong levels of evidence. Other immunomodulators implicated include tacrolimus, an calcineurin inhibitor, and interferon β-1α, used in multiple sclerosis treatment.

6. Hormonal Medications

Hormonal therapies can significantly impact hair growth patterns. Birth control pills, hormone replacement therapy, and thyroid medications are all known to potentially cause hair loss. These medications alter the hormonal milieu that regulates hair growth cycles, particularly affecting androgen-sensitive hair follicles.

Many women experience telogen effluvium when starting or discontinuing hormonal contraceptives, as the shift in hormone levels can trigger a synchronized shedding event. Similarly, thyroid medication adjustments can temporarily disrupt hair cycling until a new equilibrium is established.

7. Retinoids

Acne medications containing vitamin A derivatives (retinoids) have been implicated in hair loss. These medications affect cell growth and differentiation throughout the body, including in hair follicles, potentially leading to premature entry into the telogen phase. One common example is isotretinoin.

8. Weight Loss Drugs

Weight loss medications, such as Wegovy (semaglutide), can contribute to hair loss through multiple mechanisms. Some may directly affect hair follicle cycling, while others might cause nutritional deficiencies that indirectly impact hair growth. Additionally, rapid weight loss itself-regardless of medication use-can trigger telogen effluvium.

Management of Medication-Induced Hair Loss

The primary approach to managing medication-induced hair loss is identifying and, when possible, discontinuing the causative agent. For most patients, hair regrowth occurs within several months after stopping the medication. In cases where the medication cannot be discontinued due to medical necessity, dose reduction may help minimize hair loss while maintaining therapeutic benefit.

For ongoing treatments like chemotherapy where hair loss is expected, various scalp cooling techniques may help reduce the severity of hair loss. Additionally, topical minoxidil may be prescribed to stimulate hair growth during and after treatment. Minoxidil works for various types of hair loss, including both telogen and anagen effluvium, though the exact mechanism remains poorly understood.

Conclusion

Medication-induced hair loss represents a significant concern for patients across multiple therapeutic categories. While chemotherapy drugs are most commonly associated with severe hair loss, many commonly prescribed medications-including antibiotics, psychiatric drugs, cardiovascular agents, and hormonal therapies-can also cause this distressing side effect. Understanding the mechanisms, timing, and presentation of drug-induced alopecia is essential for proper diagnosis and management.

The good news for most patients is that medication-induced hair loss is typically reversible once the causative agent is discontinued. Healthcare providers should consider the potential for hair loss when prescribing medications, particularly in patients for whom this side effect may significantly impact quality of life or treatment adherence. By recognizing the medications associated with hair loss and their mechanisms, clinicians can better counsel patients and implement strategies to minimize this adverse effect when necessary.

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