What are the side effects of modafinil?

Of course it varies and if you want a link with a mind-numbing list like the end of a drug commercial, I've added one below. However to be more helpful I will characterize the side effects into major effects for most people. All of this multiplies in the face of other stimulants including caffeine.

Psychological
Though modafinil can initially be somewhat euphoric and social, it is inevitably neither. Regular use is likely to make you impatient and easily irritated.

Pulmonary
Modafinil can increase or throw off your heart beat. If you have any pathology here it could be a serious matter; stay away, it's not a well researched area yet. Otherwise don't freak out, just dose down at the first sign of a rapid or trembling heart beat..

Sex
A helper for neither foreplay nor ejaculation.

Coordination
Modafinil will not win any Olympic Medals, it builds a rhythm suitable to concentration, not athletic flow.

Cramps
Modafanil can cause fingers and toes to lock up, a very scary phenomena at first yet not shown to be anything particularly life threatening. Take it as a sign to back off and consider alternative nootropics.

A large population will experience none of this, don't be surprised if you are not experiencing side effects and don't let their absence be a rationale for over use.

It depends what you are using it for and how you plan to move forward.

If you are a shift worker or have chronic fatigue syndrome you are going to want to manage for long term effects, you'll be taking it up to 5 times a week (always take a couple of days off) and you want to get away with the minimal dose that will keep you awake, that's going to be 200mg for most people but 400mg is possible after a month of usage. taking more than this is serious business, even with a relatively benign drug like moda, make sure you have the medical history for this especially cardio health and monitor closely.

if you are taking moda for an exam or project a 1/2 (100 mg) will get you through a day if you don't eat much; a full 200 mg is ok, don't do more without an a.d.d. diagnosis.

whatever you do stay away from caffeine and other stimulants.