Re: what effect do alcohol, cocaine and codeine have on bloods viscosity?

hi Laura,

First, I recommend that you read this previous MadSci post about blood viscosity. It tells us that the main factor influencing blood viscosity is the percentage volume of red blood cells. So for a substance to affect blood viscosity, it has to exert some effect on cell number, cell volume or cell aggregation. The effects will vary depending on the dosage and whether intake is occasional or frequent. Other factors will include age and any medical conditions of the subjects.

Starting with alcohol, a PubMed search using "blood viscosity" AND alcohol throws up 385 references. It seems that moderate alcohol intake has little effect on blood viscosity - see for instance this study. However in a less controlled study (before and after a dinner party!), an increase in viscosity was observed. This was attributed to an increase in haemoconcentration - in other words, a reduction in plasma volume leading to a higher concentration of cells. Greatly increased viscosity is definitely observed in cases of chronic alcohol consumption and alcohol-related disease, as in this paper and binge drinking was shown to increase blood viscosity by causing platelet aggregation. Of course, we've all heard that moderate red wine consumption is "good for the blood" and that would appear to be borne out by this study, in which platelet aggregation was actually decreased.

Turning to cocaine (figuratively speaking of course), we get only 4 PubMed references. This study found that long-term cocaine abuse increases blood viscosity by triggering transient erythrocytosis - an increased number of red blood cells, as well as increased platelet aggregation.

I was unable to find good references involving the effect of codeine on blood viscosity, so there's a starting point for your research project. Codeine is an opiate derivative (it's actually methylmorphine), so we might get a clue as to its effects by searching for papers on other opioids, such as heroin. One study finds that viscosity is higher in chronic heroin users, due to an increase in red blood cell number and changes in cell morphology. On the other hand, morphine treatment of red blood cells in vitro led to a small decrease in viscosity. Codeine is chemically an alkaloid and perhaps I'll leave the literature search for alkaloids and viscosity as an exercise for you.