Dietary supplements are commercially available manufactured products used as an addition to the normal diet and involve vitamins, minerals, herbs (botanicals), amino acids, and various other products. With the use of a cross-sectional survey, the present paper intended to analyze dietary supplement usage and its health and sociodemographic determinants among attendants of primary health care centers in Abha City, southwestern Saudi Arabia. The sample was selected randomly using the two-stage cluster sampling technique. The study included 438 participants (115 males and 323 females). Their ages ranged from 18 to 59 years, with an average of 36.2 ± 11.7 years. The study showed that 330 people used dietary supplementation, giving a prevalence of 75.3% (95% CI: 71.1–79.2%). The most commonly used supplements were multivitamins (215, 65.2%), specific vitamins (60, 18.2%), and mineral pills (38, 11.5%). Advice from health care workers was the most frequent reason for using dietary supplements (49.4%). The majority (71.2%) reported feeling a better quality of life after using dietary supplements. The most frequent disadvantages of using dietary supplements were constipation and headache (30%) and the most frequent advantage was increasing appetite (59.8%). The people who most frequently recommended the use of supplements were health care workers (190, 57.6%), followed by friends or family members (62, 18.8%), and people on social media (43, 13%). Females had a significantly higher probability of using dietary supplements than males did (Cor = 2.0, 95% CI = 1.21–3.27), and those with a chronic disease had a considerably higher likelihood of using dietary supplements (cOR = 3.48, 95% CI = 2.04–6.06). Age, educational level, and marital status were not significantly related with dietary supplement usage. In conclusion, health care workers should focus on females and persons with chronic diseases in their practice. They should provide them with evidence-based advice regarding the use of dietary supplements. Continued medical education training programs tailored to the needs of health care staff addressing this issue should be provided. New guidelines should be developed to help health professionals to provide their patients with comprehensive care at the primary health care level.