Elisabeth Kirsch brought this action against Picker International, Inc., claiming that x-ray treatments administered with Picker machines caused her to develop skin cancer. The district court1 directed a verdict in Picker’s favor at the close of the plaintiff’s case. Kirsch appeals and urges that two issues should have been submitted to the jury: whether Picker failed to warn the attending physician of the cancer risks associated with x-ray therapy; and whether Picker failed to give a similar warning to Kirsch. We affirm.
At the age of twelve, Kirsch developed a mild case of acne, and her mother took her to Dr. Robert Murphy, a dermatologist. Over the following two years, she received x-ray treatments some sixteen or twenty times, according to different witnesses. This therapy was administered with two machines manufactured by Picker. In 1976, Kirsch noticed a problem with her eyebrows. In March, 1979, a lesion on her cheek caused her to see a doctor and she was diagnosed as having skin cancer. She alleges that the cancer was caused by the Picker machines.
Dr. Murphy stated that he had warned Kirsch's mother of the possibility of skin cancer, but this was vigorously denied by Kirsch and her father. Both denied receiving warnings from any source. There was *671testimony from several witnesses that Dr. Murphy would have known of the possibility of skin cancer developing after x-ray treatment, as this risk was well known in the medical profession. We will discuss further details in the evidence as they become pertinent to the issues.
The district court directed a verdict at the close of plaintiffs evidence and commented from the bench that there was a lack of evidence of failure to warn, a lack of evidence that the failure caused injury to Kirsch, and evidence of general knowledge in the medical community that x-ray radiation caused cancer. Further, the court relied on evidence that x-ray machines were produced for use only by doctors and competent operators.
On appeal Kirsch argues that there was a question of fact as to whether Picker, as manufacturer of the x-ray, adequately warned Dr. Murphy and Elisabeth Kirsch. The parties agree that these issues must be decided under Missouri law.
I.
We first deal with the duty that Picker owed to the plaintiff. Kirsch argues that Picker should have furnished a patient product information sheet warning her of the dangers of x-ray therapy. Missouri courts have held that in cases involving prescription drugs, the manufacturer has “a duty to properly warn the doctor of the danger involved.” Krug v. Sterling Drug, Inc., 416 S.W.2d 143, 146 (Mo.1967) (citations omitted). The physician acts as a “learned intermediary” between the manufacturer and the patient. Sterling Drug, Inc. v. Cornish, 370 F.2d 82, 85 (8th Cir.1966). Thus, a warning to the doctor is deemed a warning to the patient; the manufacturer need not communicate directly with all ultimate users of prescription drugs. See Johnston v. Upjohn Co., 442 S.W.2d 93, 95 (Mo.Ct.App.1969).
Prescription drugs and x-ray machines are marketed in similar fashion. As the plaintiffs expert testified, radiation therapy equipment is not sold directly to the general public but is available only to qualified professionals. Missouri law is clear with respect to prescription drugs, and these principles apply to x-ray equipment that can be utilized only at the direction of a physician. See Terhune v. A.H. Robins Co., 90 Wash.2d 9, 12-17, 577 P.2d 975, 977-79 (1978) (en banc). Thus, the manufacturer has a duty to properly warn only the doctor of the dangers associated with radiation therapy. The plaintiff was, therefore, not entitled to have a jury consider whether Picker was liable for failing to warn her directly of the cancer risks in radiation therapy.
II.
The second issue is whether Kirsch made a submissible case on Picker’s failure to warn Dr. Murphy. We have had frequent occasion to discuss the standard for reviewing directed verdicts. See Crues v. KFC Corp., 729 F.2d 1145, 1148 (8th Cir.1984). The standard is the same under federal and Missouri law. Hladyshewski v. Robinson, 557 F.2d 1251, 1252 (8th Cir.1977). “[A] directed verdict should be granted only when all the evidence points one way and is susceptible of no reasonable inferences sustaining the position of the nonmoving party.” Dace v. ACF Industries, 722 F.2d 374, 375 (8th Cir.1983) (quoting Decker-Ruhl Ford Sales v. Ford Motor Credit Co., 523 F.2d 833, 836 (8th Cir.1975)), rehearing denied, 728 F.2d 976 (8th Cir.1984) (per curiam).
Under this standard, we cannot conclude that the district court erred. The plaintiff has the burden of showing that the absence of a warning caused the injury. See Missouri Approved Instruction No. 25.05 (3d ed.1981). Picker’s failure to warn Dr. Murphy could not have been the proximate cause of Kirsch’s injury if Murphy was already aware of the cancer risks associated with radiation therapy. See Strong v. E.I. DuPont de Nemours Co., 667 F.2d 682, 687 (8th Cir.1981); Restatement (Second) of Torts § 388 comment k (1965); id. § 402A comment j. Thus, the issue narrows to whether there was evidence from which the jury could have found that Dr. *672Murphy did not know of the cancer dangers posed by the Picker machines.
The record contains no direct proof that Dr. Murphy did not know of the risks in treating acne with x-rays. Jack Kirsch, the plaintiffs father, testified that: neither Dr. Murphy nor a Picker representative warned him of the cancer risks; the Kirsch’s had a practice of discussing family medical matters; and Mrs. Kirsch did not mention to Mr. Kirsch any warnings from Dr. Murphy concerning cancer risks. Similarly, Kirsch denied receiving any warnings. She also testified that her mother had not told her of any warnings from Dr. Murphy. Viewed in a light most favorable to the plaintiff, this evidence shows only that neither Dr. Murphy nor Picker warned Kirsch or her parents. This showing is not the same as proving that Dr. Murphy did not know of the risk.
The record does, however, contain considerable evidence that Dr. Murphy knew of the cancer risks:
(1) Dr. Murphy's answers to interrogatories revealed that he warned Mrs. Kirsch: “The explanation as to the possibility of the development of skin cancer was included in general discussions with Elisabeth Kirsch’s mother in relation to the affects [sic] of treatment and it was explained that the development of skin cancer was a possibility.” (R. 25).
(2) Plaintiff’s expert, Dr. Chandler, testified that he believed dermatologists using radiation therapy in 1962 and 1963, including Dr. Murphy, were aware of the risks of skin cancer. Dr. Chandler was not personally acquainted with Dr. Murphy. Chandler also testified that the cancer risks associated with radiation have been known since the turn of the century.
(3) Plaintiff’s expert, Dr. Hall, testified that the cancer risks attendant to radiation therapy were generally known by the medical profession in 1962 and 1963.
(4) Plaintiff’s expert, Roy Ackerman, testified to his belief that Dr. Murphy would have known of the skin cancer risks.
When viewed in a light most favorable to plaintiff, there simply is no evidence that Dr. Murphy did not know of the danger in using radiation therapy. On the contrary, the only evidence is that he had such knowledge. Any failure to warn by Picker could not have been the proximate cause of Kirsch’s injuries. For this reason, the district court did not err in directing a verdict.2
We affirm the judgment of the district court.
. The Honorable Joseph E. Stevens, Jr., United States District Judge for the Western District of Missouri.
. Kirsch also argues Picker's warnings to Dr. Murphy were diluted by over-promotion. This argument has no support in the record and fails on proximate cause grounds as well.