Two Months of Daily Cannabis Use Did Not Damage Immune Function in Healthy Adults | Research

The takeaway

Healthy adults who smoked cannabis daily for 64 consecutive days showed no decline in immune function, and some initially low immune markers actually normalized over the study period.

Read this if you have heard that cannabis suppresses the immune system and want to see what controlled human research actually found.

T-cell counts rose from 951 to 1,875 cells/mm3 over 64 days of daily cannabis use

What the researchers found

Twelve healthy adults smoked cannabis daily for 64 consecutive days in a controlled hospital setting while researchers tracked multiple immune markers.

B-cell counts, initially lower than controls, increased to normal levels over the study period. T-cell counts followed the same pattern, starting significantly below controls and rising to normal by day 63. The ability of lymphocytes to respond to immune challenges (PHA stimulation and allogeneic cell response) was normal at baseline and remained unchanged throughout.

Immunoglobulin levels (IgG, IgA, IgM) stayed within normal ranges. Four subjects showed increased IgE levels, though none showed signs of allergic reactions. The researchers concluded that short-term chronic cannabis use did not produce substantial adverse effects on either B or T cells in young healthy adults.

Why it matters

Earlier lab studies using isolated cells had suggested cannabis might suppress immune function. This study tested that hypothesis in living humans under controlled conditions and found no meaningful immunosuppression, an important counterpoint to the in vitro evidence.

The numbers in context

Baseline T cells: 951 cells/mm3 (controls: 2,010). By day 63: 1,875 cells/mm3. Baseline B cells by surface immunoglobulins: 338 cells/mm3 (rose to 485). IgG: 1,064, IgA: 166, IgM: 96, all within normal ranges. Duration: 64 consecutive days of daily use.

How the study worked

Twelve healthy adults who were experienced cannabis smokers were hospitalized and smoked cannabis daily for 64 consecutive days. Researchers measured B and T cell subpopulations, lymphocyte proliferative responses to PHA and allogeneic cells, and serum immunoglobulin levels at multiple time points.

What this study cannot tell us

Only 12 participants, all healthy young adults who were already experienced cannabis users. The 64-day window may not capture effects that emerge over years of use. Baseline immune values were already lower than controls, raising questions about pre-existing differences.

How to read the evidence

A controlled observational study with daily monitoring, but only 12 participants and no randomization to cannabis vs. no cannabis.

When this study was published

Conducted in 1976. The cannabis used was substantially lower in THC content than modern varieties.

The bigger picture

This study was part of a larger scientific debate in the 1970s about whether cannabis suppressed immunity. Test-tube studies had shown THC could inhibit immune cell function, but this and other in vivo studies suggested the human immune system compensates effectively during actual cannabis use.

Questions still open

Why were baseline B and T cell counts lower than controls before the study began? Would immunocompromised individuals respond differently? What explains the IgE increases in four subjects?

Common questions

Did cannabis suppress immunity in this study?

No. Both B and T cell counts remained normal or increased, and immune response tests showed no decline over 64 days of daily use.

Why did some immune markers start low?

Baseline T and B cell counts were below control values before the study began. The researchers noted these normalized during the study, but the reason for initial low values was not clear.

Read the original research

Intact humoral and cell-mediated immunity in chronic marijuana smoking.

The Journal of allergy and clinical immunology, 58(4), 483-90

View on PubMed ↗

Citation

Rachelefsky, G S; Opelz, G; Mickey, M R; Lessin, P; Kiuchi, M; Silverstein, M J; Stiehm, E R. (1976). Intact humoral and cell-mediated immunity in chronic marijuana smoking.. The Journal of allergy and clinical immunology, 58(4), 483-90.