Is it possible that a person with hiv that has already progressed to aids can lessen the disease by taking antiretroviral drugs?

Yes indeed: Especially if previous treatment of the patient or the virus in a previous individual has not caused resistance, recovery is generally good.

AIDS Medicines: Almost all humans living with HIV can be treated with a cocktail of the HIV medications. This approach, even when started on someone who has progressed to the point of having aids, can suppress the virus, allow the immune function to recover, and to regain the ability to live a full and normal life. So, yes, of course. There is a miracle underfoot in the communities affected by hiv.