One useful point in the phentermine headache article is that weight-loss efforts themselves can sometimes contribute to the symptom. Significant calorie restriction, skipping meals, or suddenly changing carbohydrate intake may trigger headaches in some people. Sleep disruption is another factor because phentermine's stimulant effects can make falling asleep more difficult. The article therefore looks at both the medication and the surrounding lifestyle changes. https://valhallavitality.com/blog/can-phentermine-cause-headaches-what-you-should-know