Prozac is available in capsules of 10, 20, or 40 mg. It may also be dosed in a single weekly capsule of 90 mg. The maximum dosage of Prozac that is safe for you depends on many factors, including age, weight, current health, other medications, and symptoms. Your provider will prescribe the lowest effective dose of Prozac for your needs. Prozac takes time to build up in your system, so it may take time to notice benefits. Do not increase your dose of Prozac without your provider’s approval. This could result in overdose or other serious complications.