How long does the drug Lupron remain in system as I am experiencing severe headache symptoms?

Lowering your intake should be done by Doctor and can take a while, according how much you take ahd how well you do on withdrawing off.
Good luck my friend

Lupron (leuprolide acetate) Injection, Solution can also have significant side effects that may stay in your system for weeks, even months after discontinuing use.

Headaches, migraine are its side effects, there have been remedies to reduce the side effects:

Do not take aspirin or products that contain aspirin. Do not drink alcohol. Avoid sun exposure. Contact your doc./pharmacist if you experience urinary retention, inability to urinate, weakness, numbness or tingling in arms or legs and changes in vision.

Source: https://healthfully.com/side-lupron-injections-prostate-cancer-5052800.html