Are you implying his drug use had something to do with dying of a stroke at 53?
"He clearly descended into abuse after his fourth wife left him in the early 1970s. Afterward, according to Kyle Arnold’s biography, he was taking speed by the handful. “He stuffed his refrigerator with thousand-pill jars of amphetamines” and “told his mother he consumed a thousand-pill jar per week.”" https://www.thefix.com/philip-k-dick-s-high-life
"Conclusion Increases in stimulant drug abuse may increase the rate of hospital admissions for strokes and stroke-related mortality." https://jamanetwork.com/journals/jamapsychiatry/fullarticle/...
Judging from his complaint of failing eyesight the day prior to his death [1], it sounds like a common embolism. Considering Atherosclerosis is the number one cause of death in the developed world [2], it's not like we need to search for a likely cause.
I'd argue that it's likely he was going to die around this age wether he used drugs or not, but the drug use gave him a more pleasurable experience throughout his years.
It reminds me of how the cause of death for Adrian Lamo is officially "undetermined", but the medical examiner notes serum potassium and creatinine levels that are so high (in my informed opinion) that they probably can only be described as "kidney failure" or "lethal injection".