Theresa started using amphetamines to try to lose weight. After taking them for two months, she found not only that the weight was coming off, but also that she was feeling great and had lots of energy—so she kept taking them. A little over a year has passed, and Theresa finds that now she needs to take more and more of the drug to feel any increase in energy or uplift in mood. In addition, if she goes for any period of time without having the drug in her system, she feels awful. These frequently occurring "crashes" are preventing her from spending time with her friends. Theresa most likely has a(n):

Stimulant use disorder

Explanation:

Stimulant use disorder  is the disorder in which amphetamine kind of substance is taken by a person which causes exploitation being a stimulant .It causes severe damage, impairment or distress in mind and body of stimulant consumer.

It leads to losing appetite, high physical activity, heating effect in body, high alertness, high blood pressure and various related medical issues due to chemical reaction .

According to the question,Theresa can be considered experiencing stimulant use disorder as she consumed amphetamine for losing weight .This led to different chemical reaction that made her dependent upon this drugs as it gave her rapid energy for physical activities .Thus, she feels restless if she does not get this stimulant and does not spend time with others because of stimulation in behavior.