Malawi's Option B+ program is based on a 'test and treat' strategy that places all HIV-positive pregnant and lactating women on lifelong antiretroviral therapy. The steep increase in patient load placed severe pressure on a health system that has struggled for decades with inadequate supply of health care workers (HCWs) and poor infrastructure. We set out to explore health system barriers to Option B+ by asking HCWs in Malawi about their experiences treating pregnant and lactating women. We observed and conducted semi-structured interviews (SSIs) with 34 HCWs including nine expert clients (ECs) at 14 health facilities across Malawi, then coded and analyzed the data. We found that HCWs implementing Option B+ are so overburdened in Malawi that it reduces their ability to provide quality care to patients, who receive less counseling than they should, wait longer than is reasonable, and have very little privacy. Interventions that increase the number of HCWs and upgrade infrastructure to protect the privacy of HIV-infected pregnant and lactating women and their husbands could increase retention, but facilities will need to be improved to support men who accompany their partners on clinic visits.