Retail medicine outlets serve as the first point of contact for most Ghanaians seeking treatment for common ailments. However, weak regulation has led to the widespread dispensing of antimicrobials without a prescription in community pharmacies and over-the-counter medicine shops (OTCMS), fueling antimicrobial resistance (AMR). This cross-sectional study assessed the sale of prescription-only antimicrobials for common self-limiting conditions that do not require antimicrobial therapy in Tamale, northern Ghana. Using the simulated patient (SP) method, adult male actors presented with symptoms of urinary tract infection, upper respiratory tract infection, and acute diarrhoea. Three escalating levels of demand were employed to evaluate dispensing practices without a prescription. A total of 35 community pharmacies and 25 OTCMS were visited three times each, resulting in 180 SP visits. In community pharmacies, pharmacists were the most frequently encountered staff (34.3%), while medicine counter assistants predominated in OTCMS (44.0%). The overall prevalence of dispensing antimicrobials without a prescription was alarmingly high at 91.7% (165/180). Antimicrobials were commonly sold at the first level of demand, 64.8% in community pharmacies and 86.7% in OTCMS. Watch group antibiotics were more frequently dispensed in pharmacies (45.8%), whereas Access antibiotics dominated in OTCMS (47.3%). The most dispensed agents were ciprofloxacin (19.6%), amoxicillin-clavulanic acid (14.4%), and doxycycline (11.0%). This study reveals widespread violations of national regulations governing antimicrobial sales, particularly in OTCMS where such sales are illegal. Urgent implementation of antimicrobial stewardship programmes, stricter enforcement of regulations, and targeted staff training are recommended to curb irrational antimicrobial use and combat AMR in Ghana.