Take this medication exactly as it was prescribed for you. Do not take the medication in larger amounts, or take it for longer than recommended by your doctor. Follow the directions on your prescription label.
Taking high doses of phentermine over long periods of time can cause severe skin problems, sleep problems (insomnia), personality changes, and feeling hyperactive or irritable. Take this medicine with a full glass of water. It is best to take phentermine on an empty stomach before breakfast, or at least 10 to 14 hours before bedtime.
Phentermine should be taken only for a short time, such as a few weeks.
Do not crush, chew, break, or open an extended-release capsule. Swallow the pill whole. It is specially made to release medicine slowly in the body. Breaking or opening the pill would cause too much of the drug to be released at one time.
You may have withdrawal symptoms when you stop using phentermine after using it over a long period of time. Do not stop using this medication suddenly without first talking to your doctor. You may need to use less and less before you stop the medication completely.
Do not take phentermine in the evening because it may cause sleep problems (insomnia).
Stop taking phentermine if you have increased hunger or if you otherwise think the medication is not working properly. Do not take more phentermine for an increased effect. Taking too much of this medication can cause serious, life-threatening side effects.
Phentermine may be habit-forming and should be used only by the person it was prescribed for. Keep track of how many pills have been used from each new bottle of this medicine. Phentermine is a drug of abuse and you should be aware if any person in the household is using this medicine improperly or without a prescription. Store phentermine at room temperature away from moisture and heat.