1. Included trials with no data suitable for our meta‐analysis.

Trial	Findings
Abbott 1968	Therapeutic trial. The authors write: "with regard to the comparative results with the two preparations, there were virtually no differences at all in respect of any of these individual symptoms" [p 444]. The only numerical data reported were the severity of "sore throat in patients with a common cold" [their Table 1 on p 443]. It is not clear how long a delay there was between the onset of symptoms and the initiation of treatment. "The doctors taking part in the trial were asked to treat families in order, as colds appeared during the course of the winter" [p 442]; thus it seems that the doctor gave tablets only when he or she met the patient rather than patient keeping tablets ready at home for use when symptoms started.
Asfora 1977	Therapeutic trial. The author writes: "a double‐blind trial was conducted in which the preparations, numbered 1 and 8, were given to alternate patients as they presented themselves. .. When 42 patients had received substance No. 1 and 41 patients had received No. 8, there was no longer any point in continuing the double‐blind trial, since in view of the clinical progress of the patients there was not the slightest doubt that substance No. 1 was vitamin C and No. 8 was the placebo" [p 224]. Thereafter the trial was continued as an open trial comparing vitamin C with other drugs.
Brown 1945	Therapeutic trial. Of the 206 "nasal colds", 62% (76/123) of the vitamin C group had a cold being cured overnight whereas 37% (31/83) of the placebo participants had colds that were cured overnight (P = 0.06). There was no difference in the curing of 92 "throat colds" (35/56 versus 22/36, respectively). The great difference in the distribution of participants is not consistent with reported alternate allocation.
Elliot 1973	Prophylactic trial. The authors write: "There was no consistent difference between groups in the incidence of runny nose or sneezing. Man‐days of morbidity for hoarseness, sore throats, non‐productive coughs, and productive coughs was 36, 107, 42 and 72 in the placebo group with only 37%, 28%, 40% and 31% as much morbidity in the ascorbic acid group. The Wilcoxon Sequence Test with a one tailed test rejected the null hypothesis of equal effectiveness of ascorbic acid and placebo for sore throats and productive coughs (P = .0155 and .0327) but not for hoarseness or non‐productive coughs" [p 12] (Hemilä 2004).
Regnier 1968	Therapeutic trial. The author writes: "I initiated a double‐blind study using ascorbic acid alone, ascorbic acid plus bioflavonoids, flavonoids only and, fourthly, a lactose placebo with the two "vitamins" present either alone or together in 200 mg quantities. It was shortly obvious that there was no need to continue double‐blind techniques. The continued studies were done by the single blind method... " "The 22 subjects mentioned have been studied systematically and under conditions which were as controlled as is possible in a clinical investigation of an infection such as the common cold. Some acted as what are commonly termed their own controls... None of the subjects was studied for less than three years... [p 950]." "Within the first 24 hours of a typical infection which the patient recognizes as his usual early symptoms of a cold, and the sooner the better, the beginning dose of ascorbic acid or 0.6 or 0.625 g is taken every three hours" (p 950). The author reports that "in 50 colds the treatment consisted of ascorbic acid alone ... the colds were nicely suppressed in 45 [of the 50]... In 22 of 24 instances in which the lactose‐filled capsules alone were taken the colds were seemingly untempered and ordinary" [p 952].
Scheunert 1949	Prophylactic trial. The common cold [Erkältungskrankheiten] was one of the outcomes and "The percentage monthly duration of people sick with the common cold [Prozentualer Monatsdurchschnitt der erkrankten Personen]" was 7.3% in the 0.02 g/d group, 7.2% in the 0.05 g/d group, 1.95% in the 0.1 g/d group, and 1.93% in the 0.3 g/d group suggesting that there were more days sick with the common cold when vitamin C doses were low. However, the data are presented ambiguously and it is a combination of incidence and duration. The methodology is not good.
Tebrock 1956	Therapeutic trial. The authors conclude "the overwhelming impression gained from the study is the singular lack of effect in altering the course of the common cold by ... the ascorbic acid". A number of tables were published but they could not be used in our meta‐analyses.