No, you should not take more than 37.5 mg of phentermine per day. The available source shows that 37.5 mg is the maximum approved daily dose for adults, and there is no official guidance supporting higher doses.
Phentermine dosing is typically kept between 15 mg and 37.5 mg per day, depending on how a person responds. The guidance also states that if the medication seems less effective over time, the dose should not be increased. Instead, it should be stopped or reassessed.
Taking more than the recommended dose can increase the risk of serious side effects. These may include fast heart rate, high blood pressure, confusion, agitation, and in severe cases, heart problems or other life-threatening complications. Even doses only slightly above the recommended range have been linked to higher risks.
Phentermine is meant for short-term use alongside diet and lifestyle changes, and the dose should always be individualized. Do not adjust your dose on your own. Speak with your doctor if you feel your current dose is not working or if you have concerns about your treatment.