Just a few thoughts coming from Leslie et al. 2019 Article Adherence to cardiovascular medication: a review of systematic reviews

"Patients who had to make co-payments for treatment were at a 28% greater risk of non-adherence, as they were less likely to collect their statins at the appropriate time [20], and similar associations were found across cohort studies of adherence to antihypertensives [30]. The impact of co-payment on adherence varied depending on the actual cost to the patient [31]."

i think we cannot generalize certain magnitude of effect it depends mainly on socioeconomic state and specially found in third world countries

Fazleh Mahomed

To answer your question, yes, the compliance and the adherence is affected by the cost of the pharmacotherapy.

It's just the anecdotal evidence, but during my 6-month-long traineeship in the local community pharmacy I've seen several situations, when patients resigned from medicines or just bought only part of the pharmacotherapy due to the cost. As Fedaa Kamaleldeen said, the magnitude of this phenomenon depends on many factors, mainly on economical situation and the costs oft the medicines.

But I don't think it occurs only in the third world countries. I will try to find some stats about it : )