In Alabama, your employer can fire you for whatever reason they want except because of your race, sex, age, religion, national origin, or disability. Also, they cannot fire you if you have a contract or "solely" because you filed a workers compensation claim. The only way you can take action against them is if you can prove the medication issue was a pretext for one of these other reasons or if you can show you had a contract, and they breached it.
You may consider consulting with an employment attorney about potential ADA issues. The fact that adipex is a weight loss medication raises a potential issue related to obesity. Obesity is not a disability under the ADA but addressing obesity is often a means of addressing other medical issues that may qualify as disabilities within the meaning of the ADA.
The EEOC recognizes that, while obesity is not considered a disabling impairment, a person with obesity may have an underlying or resultant physiological disorder, such as hypertension or a thyroid disorder. A physiological disorder is an impairment.
This seems like quite a reach given the information provided but is something to consider nonetheless.