Guanfacine - should he take it in the am or pm?

Guanfacine/Tenex/Intuniv is used for several purposes. Although the correct time to take this medicine for ADD or ADHD is prior to school in the morning, Guanfacine can definitely cause sleepy side effects. Here are the facts:
Nervous system side effects have included fatigue or a sedative effect in 33% of patients. After one year of therapy, the incidence of these side effects falls to 6%. Nervous system side effects associated with the extended-release formulation have included somnolence (38%), fatigue (14%), headache (24%), lethargy (6%).

These are high incidences of fatigue and tiredness. I recommend you talk with your son's Dr. as soon as reasonably possible. You could call this coming Monday. He or she may want to adjust the dosage of this drug or try another drug altogether.

{My sons took the old stimulant drugs that were available years ago and did very well with them. They wouldn't have received an education without them. They had no trouble with being tired. One son still must take stimulants to function even now as an adult. If I can be of any further help, please ask & I will get your question.} I hope this problem gets resolved quickly for you and your son. It's a challenge, isn't it?