Yes. Headaches can be a side-effect. Right after you smoke, especially if you've smoked a lot of weed, many people experience sort of "adrenergic" period--as if they've had a burst of adrenalin. The heart rate speeds up, blood pressure rises, vaso-constriction increases. (It's during this early window after smoking that people's heart attack risk is five times what it normally is. This is also the effect that sets off panic attacks in some smokers.) That vaso-constriction can trigger monumental headaches, and from what I've been able to observe, some strains are worse about setting this off than others. Time seemed to relieve the headache problem with my sister. Ibuprofen can be helpful, too, in helping quell some of the inflammation that results from the headache. Lay off the weed, get some rest, and make sure you're well hydrated. All those things will help the headache subside.